1. Field of the Invention
The present invention relates to a soldering ball mounting apparatus and a soldering ball mounting method, wherein soldering balls are vacuum-absorbed by a pickup head and then mounted onto a workpiece.
2. Description of the Prior Art
It is known to form bumps (protruding electrodes) on a surface of a workpiece, such as, a chip or a substrate, by mounting soldering balls onto the surface of the workpiece, heating to melt the mounted soldering balls and then cooling the molten soldering balls to solidify. In general, a large number of bumps are formed on the workpiece so that a large number of soldering balls are mounted on the workpiece.
Hereinbelow, a conventional soldering ball mounting apparatus for mounting a large number of soldering balls onto the workpiece at a time will be explained with reference to FIG. 18.
FIG. 18 is a side view schematically showing the conventional soldering ball mounting apparatus. In the figure, soldering balls 1, each as a material for a bump or a bump electrode, are stored in a container 2. Numeral 3 denotes a pickup head which is driven by up-and-down moving means (not shown) so as to be movable in the vertical directions, that is, upward and downward. The pickup head 3 has a bottom wall formed with a large number of absorber openings or holes for absorbing the soldering balls 1 thereat by a vacuum suction force when the pickup head 3 is lowered from an initial position to a given low level. The pickup head 3 is further driven by horizontally-moving means (not shown) so as to be movable in the horizontal directions. Specifically, the pickup head 3 moves from the initial position to just above the workpiece, such as, a substrate 5 which is firmly clamped in position by a clamper 6. The pickup head 3 is then lowered to a given low level and releases the absorbed soldering balls so as to mount them on given locations on the surface of the substrate 5.
As appreciated, it is necessary that the soldering balls 1 be picked up by all the absorber holes formed at the bottom wall of the pickup head 3 and all the picked-up soldering balls be mounted on the surface of the substrate 5. Accordingly, in the conventional technique, a camera 4 is disposed under the moving path of the pickup head 3 so as to monitor the bottom wall of the pickup head 3 from below. Specifically, image data sent from the camera 4 are processed to determine whether all the absorber holes hold the soldering balls 1. If positive, the pickup head 3 further moves to just above the substrate 5 and is then lowered to mount the soldering balls 1 on the substrate 5.
However, in the foregoing conventional technique, determination of presence or absence of the soldering ball which is small, is difficult due to, for example, flickering or noise in the image data sent from the camera 4 so that a determination error is liable to occur. Further, in general, as described above, a large number (for example, several tens or more) of the soldering balls 1 are vacuum-absorbed by the pickup head 3. Thus, it takes a considerable time to check whether the soldering balls 1 are absorbed or not with respect to all the absorber holes. This deteriorates the working efficiency.
Further, all the soldering balls picked up by the pickup head are not always mounted onto the workpiece due to a mounting error. Accordingly, it is possible that some soldering balls may remain attached to the corresponding absorber holes of the pickup head. In this case, the processed workpiece becomes defective as lacking some soldering balls thereon.
However, in the conventional technique, there has been no means provided for automatically detecting such a mounting error so that problems, including the production of the defective workpieces, caused by the mounting error, are liable to occur.